The invention relates to a machine for feeding a food product to a device for placing the food product in contact with a coagulation product, with a view to coating said product with a hardened material acting as an outer skin also referred to as a “casing”, whether the casing is natural or not.
The food products concerned are particularly long, flexible products subject to natural bending. Such products are defined as any product wherein an outer casing is liable to change the shape, subject to the strain exerted by said casing.
In this way, the invention applies to sausages, black or white puddings, and other food products in particles placed in a casing.
A number of these products are prepared by co-extrusion which is a particular form of extrusion.
The principle of food product co-extrusion is described in NL 6909339. A surface of a strip of food paste is coated with a collagen surface coating by co-extrusion. Following extrusion, the coated strip is guided to a coagulation bath to fix the outer casing.
Under the influence of the coagulation solution, the collagen coagulates and/or precipitates. A strip of food paste is thus at least partially coated with a solid outer collagen casing.
In addition to proteins such as collagen, in the food industry, polysaccharides, such as alginate, are also frequently used as a coating agent for foods such as, for example, sausages. The term alginate refers to a group of natural polysaccharides extracted from algae. In the presence of alkaline-earth metals (such as magnesium alginates, calcium alginates), gels may form relatively easily. Collagen and alginate may also be used in combination, as described in WO 2006/135238 A2.
Studies have demonstrated that the gelling of alginates under the effect, for example, of calcium takes place due to the formation of a three-dimensional structure (cf. egg-box model). When the alginate is converted into this three-dimensional structure, a relatively solid gel is created. Such a gel particularly suitable for use as a casing for sausages for example.
In co-extrusion, the casing is frequently extruded on a food in the form of a strip of paste used for manufacturing sausages. Guiding the coated extruded strip in a salt bath containing calcium ensures the setting of the coating which solidifies somewhat. Due to the presence of calcium, the coating agent, for example alginate, gels quickly.
The extruded food may be reinforced further by subsequently adding calcium on the food product.
However, one drawback is that the initial strength/solidity of the alginate gel weakens over time, for example within 24 hours, due to metal chelates (for example, phosphates) present in the food paste dissolving the divalent ion, for example calcium, bound with the gelling agent. The elimination of divalent ions from the gel induces swelling and alteration of the gelling agent. In the worst cases, the gel disappears completely and, consequently, the food is no longer stable and falls apart.
A further drawback of alginate gel is that the gel per se does not actually adhere to the food paste. Consequently, the cooking characteristics of a co-extruded food product, for example a sausage, are such that, during cooking, the gel does not shrink with the food paste and the cooking heat is not distributed by the food. This results in an accumulation of heat in the gel coating, inducing undesirable deformation and discolouration of the coating due to the evaporation of the moisture in the coating. Moreover, air bubbles may form between the food paste and the casing during cooking, giving rise to a less attractive product and/or insufficient cooking, at least locally.
In view of the above, it was deemed necessary to stabilise and increase the strength (resistance/solidity) of the alginate gel applied to the food paste to enhance the shelf-life.
Increasing the number of divalent ions, for example calcium, strontium, barium or combinations thereof, has been envisaged in the prior art. However, a greater number of divalent ions give rise to variations in taste, for example a bitter taste, possibly relatively high salt consumption and equipment corrosion.
Moreover, it is necessary to increase the adherence between the gelling agent and the food paste and also the cooking characteristics of the product.